Metal hexacyanoferrate coated silver halide elements and process for making lithographic images

ABSTRACT

An element suitable for preparing a long lived gelatin lithographic printing plate is prepared by coating a gelatinosilver halide emulsion layer with a hexacyanoferrate. In process of use, the element is exposed to actinic radiation, developed in a conventional developer, and activated with a cupric ion solution to form a lithographic image which accepts ink in the exposed areas and water in the unexposed areas. Novel activating solutions for the silver halide are provided. The resulting printing plates are capable of yielding many thousands of impressions.

llnited States Patent Blaine 51 Jan. 18,1972

[54] METAL HEXACYANQFEWATE @OATED SILVER HALHDE ELEMENTS AND PROCESS FORMAKING LHHOGRAPEMC IMAGES [72] Inventor: Ralph Kingsley Blake,Westfield, NJ.

[73] Assignee: E. l. du Pont de Nemmrrs and tllompany,

Wilmington, Del.

22 Filed: Aug. 4, 1969 21 Appl.No.: 847,399

3,113,023 12/1963 Mellan ..96/33 Nadeau ..96/33 Kluptel ..96/33 [5 7]ABSTRACT An element suitable for preparing a long lived gelatin1ithographic printing plate is prepared by coating a gelatino-silverhalide emulsion layer with a hexacyanoferrate. In process of use, theelement is exposed to actinic radiation, developed in a conventionaldeveloper, and activated with a cupric ion solution to form alithographic image which accepts ink in the exposed areas and water inthe unexposed areas. Novel activating solutions for the silver halideare provided. The resulting printing plates are capable of yielding manythousands of im pressions.-

8 Claims, N0 Drawings METAL HEXACYANOFERRATE COATED SILVER l'lAlLlllDEELEMENTS AND PROCESS FOR MAEUNG lLllTHOGRAlPHlC IMAGES BACKGROUND OFINVENTION This invention relates to lithographic printing and more particularly to the preparation of lithographic printing plates. Still moreparticularly it relates to preparing improved lithographic printingplates from gelatino-silver halide emulsion layers.

Preparing lithographic plates from gelatino-silver halide emulsionlayers is well known. in one process an exposed gelatino-silver halideemulsion layer is developed with a tanning developer which converts thegelatin in the imaged areas to an oleophilic colloid. The developedgelatino-silver image may also be used to produce a lithographic plate.The silver image may be used to catalyze oxidative degradation of thegelatin in image areas, thus exposing an oleophilic underlayer.

According to the bromoil process the gelatino silver image is treatedwith a bleach which tans the gelatin in the imaged areas so that itbecomes ink-receptive. in a process disclosed in Liissig et al., US.Pat. No. 3,083,097 a silver image devoid of associated silver halide,including a gelatino-silver image, maybe converted to a lithographicimage by a process comprising the sequential steps of treating saidimage with a bleach which converts the silver image to an image of heavymetal and/or silver compounds and then reacting these compounds with analkaline solution of sparingly soluble organic compounds containing SH,-Sel-l, OH, or NH groups to form compounds which are less soluble thanthe original products of oxidation and make the imaged areas of theplate oleophilic. The prior art processes use an ordinary silver orgelatino-silver image obtained by conventional photographic processesfrom a gelatino-silver halide photosensitive stratum. These processeshave several disadvantages. They are of limited utility because theprocesses require much skill, are complex and slow, requiring fixing andwashing steps, and the plates have a relatively short press life.

This invention comprises a novel element and a process of using saidelement to rapidly and conveniently rnalte a lithographic plate having afast start printing capability and a relatively long press life.

SUMMARY OF THE lNVENTlON This invention comprises an element and aprocess of forming images therefrom. The element comprises a supportedphotosensitive gelatino-silver halide emulsion layer having in operativeassociation with its surface a stratum of hexacyanoferrate sol. Theprocess of use comprises the steps of exposing the element to actinicradiation, developing the exposed element with a conventionalphotographic developer, andtreating the developed element with a cupricion activator which converts the imaged element into a lithographicprinting plate capable of many thousands of impressions. Optionally, aphotographic developing agent may be incorporated in the emulsion.

The gelatino-silver halide emulsion layer comprises silver chloride,chlorobromide, bromide or iodobromide crystals dispersed in a gelatinbinder coated on a support to a coating weight of at least 1 mg. ofsilver halide per square decimeter. The amount of silver halide used issomewhat dependent on the results desired but at least 1 mg./dm." mustbe present to provide a lithographic image. There is no upper limit touseful coating weights but there is no advantage in using more than 100mg./dm. of silver halide. Satisfactory results are obtained with coatingweights of about 5 to 50 mg./dm. of silver halide. The emulsion may bepanchromatically sensitized.

Preferably, the emulsion is overcoated with a thin antiabrasion layer ofgelatin or similar water-permeable proteinaceous colloid containingimidazole groups. The antiabrasion layer may contain thehexacyanoferrate sol but preferably said sol is coated last over eitherthe emulsion or the antibrasion layer, if present. Suitableproteinaceous colloids that may be used in place of or in addition togelatin include casein and zein.

The hexacyanoferrate sol comprises an aqueous dispersion ofhexacyanoferrate (ll) (ferrocyanide) or hexacyanoferrate (Ill)(ferricyanide) ions with a suitable heavy metal cation. Preferredcations are copper (ll), nickel (ll), cobalt (ll), palladium (ll), andrhodium (ll). The hexacyanoferrate sol used in coating thegelatino-silver halide emulsion contains 0.005 to 0.1 mols of thehexacyanoferrate per liter. Coating adjuvants may be added to the soland complexing agents, e.g., citrate ions, are useful in controlling thefree cation concentration for optimum results.

The photosensitive element should have sufficient hardener added to theemulsion and/or antiabrasion layer and/or hexacyanoferrate sol so thatno substantial amount of colloid is transferred on printing.

The film supportfor the emulsion layers used in the novel process may bea macromolecular organic polymer. For example, a cellulose derivative,e.g., cellulose acetate, cellulose triacetate, cellulose mixed esters,etc., may be used. Polymerized vinyl compounds, e.g., copolymerizedvinyl acetate and vinyl chloride, polystyrene, and polymerized acrylatesmay also be mentioned. The film formed from the polyesterificationproduct of a dicarboxylic acid and a dihydric alcohol made according tothe teachings of Alles, US. Pat. No. 2,779,684, and the patents referredto in the specification of that patent, is suitable. Other hydrophobicfilms are the polyethylene terephthalate-isophathalates of British Pat.No. 766,290 and Canadian Pat. No. 562,672 and those obtainable bycondensing terephthalic acid and dimethyl phthalate with propyleneglycol, diethylene glycol, tetramethylene glycol or cyclohexane1,4-dimethanol (hexahydro p'xylene alcohol). Thefilms of Bauer et al.,U.S. Pat. No. 3,052,543 may also be used. The above polyester films areparticularly suitable because of their dimensional stability. Paper,especially polyethylene coated paper, and metal may also be usedassupports.

In practicing this invention the element is exposed to actinic radiationimagewise, developed to a silver image in a conventional silver halidelatent imagedeveloper, then activated in a solution containing at least0.01 mole of cupric ion per liter. The silver image may be completelyconverted to silver ion but preferably activation is continued untilpart but not all of the superficial developed silver is converted tosilver ion, with equivalent formation of cuprous ion. Preferably theactivator contains a cupric halide which reconverts developed silver tosilver halide.

After this treatment the exposed areas of the gelatin layers areoleaginous ink-receptive and the plate may be immediately placed on aprinting press.

In another use of the element of this invention the photosensitivehexacyanoferrate coated element or a similar nonsensitive silver halidefree coating of the hexacyanoferrate sol on or in a supported, suitablyhardened, hydrophilic, water-permea ble gelatin or proteinaceous coatingcontaining imidazole groups may be used as the receptor element in atransfer process. lln such a process a conventional silver image isactivated in contact with said receptor element. An ink-receptive imageis formed on the silver-free: receptor element and after separation thereceptor element may be used as a lithographic printing plate.

The element of this invention is well adapted to the preparation oflithographic plates directly from automatic phototypesetting equipment.Contact or reflex exposures may also be made to prepare plates suitablefor rapid, simple document duplication.

The activator solutions used in practicing this invention comprisecopper (Il) ion in a concentration of at least about 0.01 molar,preferably at least 0.03 molar, a halide ion capable of forming a silversalt that is at most as soluble as silver chloride which is added toprovide a concentration of about 0.01 molar to about 0.5 molar,preferably 0.0] to 0.1 molar, and, optionally, iron (III) ion in aconcentration such that the ratio of copper (ll) ion concentration toiron (III) concentration is between about 1/5 and about 1 preferablybetween lit and 30/1. The pH of the activator solution should be fromabout 0.5 to 6 and preferably between 1 and 3.

The activator solution may contain other adjuvants which improve thequality of the lithographic plate. Cyanoguanidine, l,2,3-triphenylguanidine, benzotriazole, and 1,10- phenanthroline areuseful adjuvants which may be added to the activator solution. Activatorsolutions containing cyanoguanidine and 1,2,3-triphenylguanidine giveplates which start to print more rapidly on the press than solutionswithout them. Activator solutions containing benzotriazole give improvedplates having a longer press life. The rate of activation of thesolution may be controlled by adding 1,10- phenanthroline which slowsthe activation reaction.

The following examples will illustrate the invention but are notintended to limit its scope.

EXAMPLE I A nickel (ll) hexacyanoferrate (ll) sol prepared as follows:

Solution A 0.1M Potassium citrate l ml. 0.1M Nickel (ll) nitrate ml.Solution B 0.1M Potassium hexacyanoferrate (ll) l5 ml. Saponin aqueoussolution) 1 ml. Thymol (5 g./l00 ml. of ethanol) 2 ml. Water 82 ml.

Solution A was added to Solution B in seconds with rapid stirring at 75F.

An orthosensitized gelatino-silver chlorobromide emulsion having a 70/30mole percent'bromide/chloride ratio and containing 1 l l g. of gelatinper mole of silver halide was coated at a coating weight of 88 mgJdm. ofsilver halide on a subbed polyethylene terephthalate film base preparedas described in example IV'of Alles, U.S. Pat. No. 2,779,684. The driedemulsion was overcoated with a gelatin antiabrasion layer at a coatingweight of 2.5 mg./dm. of gelatin hardened with 4.25 g. of dimethylolureaper 100 g. of gelatin. The element was then overcoated with the nickel(II) hexacyanoferrate (II) sol in red safelights as a speed of 8 feetper minute and a temperature of 75 F., then hot air dried.

A sample of the element was exposed through a halftone and line testnegative for 6 seconds with a 500-watt RSP-2 reflector photospot lamp*operated at 15 volts. The exposed sample was developed for seconds at 72F. in a conventional high pH hydroquinone/l-phenyl-3-pyrazolidonedeveloper containing 0.25 g. of benzotriazole per liter, rinsed 5seconds in water than activated without prior fixing for 30 seconds at72 F. in an aqueous bath of the following composition.

3 molar cupric nitrate solution 50 ml. 3 molar citric acid solution 50ml. 3 molar potassium bromide solution 5 ml. 1 molar iron (Ill) nitratesolution 15 ml. Water to make 1.000 ml.

3 molar aqueous orthophosphoric acid solution 10 ml. 0.5 molar aqueoustrisodium phosphate solution ml. Water to make 1,000 ml.

*Tungsten filament, placed at a distance of 50 inches.

The fountain solution was then prepared from the concentrate accordingto the following formula.

Fountuln solution concentrate 20 ml. (ium uruhlc nulutlnn (l purl byweight to I00 parts by volume of water) 20 ml. Diethylcnc glycolmonohutyl other 50 ml. Water to rnnkc L000 ml.

The plate was then inked with lithographic ink and used to print 10,000offset copies on white bond paper. The plate started to print rapidlyand all prints were of good quality.

EXAMPLE II A sample was prepared as in Example I using a cobalt (II)hexacyanoferrate (II) sol in place of the nickel (II) hexacyanoferrate(ll) sol. The sol was prepared as in example I using cobalt (II) nitratein place of the nickel (ll) nitrate. This sample, when exposed,activated, inked, and printed, as in example I, gave good copies on bondpaper.

EXAMPLE III A sample was prepared as in example I using a copper (ll)hexacyanoferrate (II) sol (prepared as in example I using copper (II)nitrate instead of nickel (Il) nitrate) as an overcoat for thegelatino-silver halide layer. Wen the sample was exposed, activated,inked, and printed, as in example I, negative offset copies wereobtained.

EXAMPLE IV A sample was prepared as in example I using the followinghexacyanoferrate sol instead of that of example I.

Solution A Water 75 ml. Gum arabic (l g./l00 water) 10 ml. 0.] molaraqueous nickel (ll) nitrate hexahydrate 5 ml. Polyacrylic acid (5ml./l00 of water) 10 ml. Solution B Water 70 ml. Gum arable (l g./l00ml. of Water) 10 ml. Polyacrylic acid (5 ml./l00 of water) l0 ml.

Solution A was added to solution B in 5 seconds with rapid stirring.

When exposed, activated, inked, and printed, as in example I, negativeoffset copies were obtained.

EXAMPLE V Example IV was repeated except that the activator solution hasthe following composition:

3 molar copper (ll) nitrate trihydrate (aqueous) 25 ml. 3 molarpotassium bromide (aqueous) 50 ml. 1 molar potassium acetate (aqueous)ml. l molar ferric nitrate nonahydrate (aqueous) 100 ml. Water to makeL000 ml.

When inked and printed as in example I, good negative offset copies wereobtained devoid of scum in unexposed areas.

EXAMPLE VI A nickel (II) hexacyanoferrate (III) sol was prepared by theprocedure of example IV using potassium hexacyanoferrate (III) in placeof the potassium hexacyanoferrate (II). An element was prepared as inexample I. This element was exposed through a /2 step wedge to a No. 2RFL photoflood operated at 35 volts at a distance of 2 feet. The exposedelement was developed in a high pH l-phenyl-B-pyrazolidinonehydroquinone developer containing 0.25 g. of benzotriazole per liter,bathed in 2 percent acetic acid for 30 seconds, washed and dried. Thesample was then bathed for 20 seconds in an activation solution of thefollowing composition:

3 molar potassium bromide solution 100 ml. 3 molar copper (ll) nitratesolution 50 ml. Water 850 ml.

The sample was then rubbed with the fountain solution of example I, theninked and printed. Good lithographic copies were obtained.

EXAMPLE VII A sample was prepared as in example VI using a nickel (II)hexacyanoferrate (II) prepared as follows:

Solution A Water 0.1 molar nickel (ll) nitrate hexahydrate (aqueous)Solution 13 Water 85 ml. 0.1 molar potassium hexacyanoferrate (11)(aqueous) Solution A was added to Solution B with rapid stirring. Thesample was exposed, developed and activated as in example VI. When inkedand printed, good copies resulted.

EXAMPLE VIII A sample was prepared as in example VII using an overcoatmade from the following solution.

Solution A 0.1 molar potassium citrate (aqueous) ml. 0.1 molar nickel(l1) nitrate (aqueous) 5 ml. Water 85 ml. Solution 8 0.1 molar potassiumhexacyanoferrate (ll) l5 ml. Saponin (10% solution in alcoho1-water) 1ml. Thymol (5 /100 ml. of alcohol 2 m1. Water 82 ml.

The sample was exposed for 3 seconds through a line and halftone testnegative with a No. 2 RFL photoflood operated at volts at a distance of40 inches. The exposed sample was developed for 30 seconds in a high pHl-phenyl-3- pyrazolidone/hydroquinone developer, water washed for 10seconds, and activated for 1% minute in an activator solution having thefollowing composition.

3 molar hopper (l1) nitrate (aqueous) 50 ml. 3 molar citric acid(aqueous) 50 ml. 3 molar potassium bromide (aqueous) 5 ml. 1 molar iron(111) nitrate (aqueous) 5 ml. Water to make 1.000 ml.

The sample was then washed and used to print 1,400 copies on an offsetoffice duplicator. The solution of example I was used. Good offsetcopies were obtained.

EXAMPLE IX A nickel (II) hexacyanoferrate (II) sol was prepared asfollows:

Solution Awas added to Solution B in 15 seconds with rapid stirring.

A high-speed orthosensitized gelatino-silver iodobromide emulsion havingabout 1.2 percent silver iodide and containing about 120 g. of gelatinper mole of silver halide, coated at a coating weight of about 25mgJdrn. on a smooth, polyethylene coated, photographic paper base wasovercoated with the sol by skim coating at a speed of 8 feet per minuteand hot air drying.

Samples were exposed through a line and halftone test negative with a500 watt RSP-Z photospot lamp operated at 15 volts at a distance of 50inches. Exposed samples were developed seconds in the developer ofexample I, rinsed 5 seconds in water, then activated for 20 seconds inan activator solution of the following composition:

3 molar potassium bromide (aqueous) 15 ml. 3 molar copper (11) nitrate(aqueous) 25 ml. 3 molar citric acid (aqueous) 25 ml. 1 molar iron (I11)nitrate nonunhydrat-e (aqueous) 25 ml. Triphenyl guanidine (1 3/100 ml.of alcohol) 50 ml. Water to make 1,000 ml.

The activated plate was water rinsed 5 seconds, mounted on an offsetoffice duplicating machine, rubbed with the fountain solution of exampleI, and used to print more than 500 offset copies using the fountainsolution of example 1.

EXAMPLE X A nickel (II) hexacyanoferrate (II) sol was prepared as fo1-lows:

Solution A Water 800 m1. Nickel (II) nitrate hexahydrate 0.75 g.Potassium citrate monohydratc 0.61 g. Solution B Water 190 ml. Potassiumhexacyanoferrate (II) trihydrate 1.06 g. Sodium octyl phenoxy ethoxysulfonate (4.2% aqueous solution) 10 ml.

Solution A was added rapidly to B with vigorous stirring.

Example IX was repeated using the: above sol as the overcoat. Anexcellent lithographic plate was obtained capable of printing severalthousand offset copies.

EXAMPLE XI Example IX was repeated using an activating solution of thefollowing composition:

Glacial acetic acid ml. Benzotriazole (1 51100 ml, of alcohol) 100 ml. 1molar potassium citrate (aqueous) 100 ml. 3 molar potassium bromide(aqueous) 50 ml. 3 molar copper (ll) nitrate trihydrate 25 m1. 1 molariron ("1) nitrate monohydrate 25 m1. Triphenyl guanidine (l gJlOO ml.olalcohol) 50 ml. Water to make L000 ml.

A good lithographic plate was obtained which has a rapid start-up on thepress without background scum.

EXAMPLE XII Example VII was repeated except that the activator solutionhad the following composition:

3 molar copper (ll) nitrate trihydrate Good lithographic ink copies wereobtained.

EXAMPLE XIII Example VII was repeated except that the activator solutionhad the following composition:

3 molar copper (ll) nitrate (aqueous) 50 m1. 3 molar citric acid(aqueous) 50 m1. 3 molar potassium bromide (aqueous) 5 ml. 1 molar iron(111) nitrate (aqueous) 5 ml. Water to make 1,000 m1.

Good lithographic ink copies were obtained.

EXAMPLE XIV A nickel (II) hexacyanoferrate sol was prepared as follows:

Solution A Water 0.1 molar nickel (ll) nitrate hexahydrate (aqueous) 20ml.

0.1 molar potassium citrate monohydrate (aqueous) 15 ml. Solution BWater 72 ml.

0.1 molar potassium hexacyanoferrate (ll) trihydratc 20 ml.

Condensation product of coconut fatty acid and diethanol amine (l g./lml. of alcohol) 8 ml.

Solution A was added to Solution B in 15 seconds with rapid stirring at75 F.

A commercial stabilization enlarging paper having developer incorporatedin the photosensitive emulsion was dipped into this sol, allowed todrain, and dried.

A sample was exposed through a'negative line and halftone imagetransparency for 10 seconds using a K&M Tri Level Point Source lampoperated at level 1 at a distance of 55 inches. The exposed sample wastreated with a basic activator solution for 35 seconds, then treated for10 seconds with the lithographic activator solution of example IX. Theprocessed sample was swabbed with the fountain solution of example I,inked, and used to print good lithographic copies.

EXAMPLE XV The emulsion of example IX was coated to a coating weight ofabout 25 mg./dm. on a smooth, polyethylene coated, photographic paperbase and dried. The emulsion layer was overcoated as in example XIV withthenickel (II) hexacyanoferrate sol of example X to which 40 grams perliter of hydroquinone and 5 grams per liter of sodium sulfite wereadded. The sample was exposed as in example XIV except that a 3 secondexposure was used. The exposed sample was processed as in example XIVand good lithographic copies were obtained.

EXAMPLE XVI A direct positive fogged silver chloride emulsion madeaccording to the teachings of Burt, US. Pat. No. 3,445,235, was coatedto a weight of 57 mg. of silver halide per square decimeter on a'polyethylene terephthalate support made IOO-watt tungsten filament pointsource lamp (General Electric Co. flash lO0T8-l5c-20v) operated at 8volts. according to example IV of Alles, US Pat. No. 2,779,684, anddried. The emulsion was then overcoated in red safelights with thenickel (ll) hexacyanoferrate (II) sol of example V at 9 feet per minuteand 100 F, then hot air dried.

A sample was exposed for 20 seconds through a positive line and halftoneimage transparency to a 500-watt RFL photoflood lamp operated at 110volts at a distance of 2 feet. The exposed sample was developed 30 sec.in the developer of example I, rinsed in water for 5 sec. and activatedfor 20 sec. in the activator solution of example IX. After treatmentwith the fountain solution of example I the plate was used to print goodpositive lithographic ink copies.

EXAMPLE XVII Solution A I 3 molar copper (ll) nitrate trihydrate(aqueous) 25 ml. 3 molar potassium bromide (aqueous) 15 ml. 3 molarcitric acid (aqueous) 25 ml. 1 molar iron (ll) nitrate (aqueous) 10 ml.Water to make 900 ml.

Solution 8 LlO-phenanthroline (l g./l00 ml.

cl'alcohol) 50 ml. l,2-bis(2-chloroethoxy)ethanol 10 ml.

The activator solution had the following formula.

Solution A 900 ml. Solution B 60 ml. Water to make l,00t) ml.

The activated plate was squeegeed dry, placed on an office duplicatingmachine, swabbed with the fountain solution of example I and used toprint several hundred ink copies. A good positive lithographic image wasobtained.

EXAMPLE XVIII A high-speed orthosensitized gelatino-silver iodobromideemulsion having 1.2 mole percent silver iodide and a gelatin to silverhalide ratio of 0.36 was coated at a coating weight of 7.2 milligrams ofsilver bromide per square decimeter on a polyethylene terephthalatephotographic film base. The em ulsion was overcoated with anantiabrasion layer comprising 10 milligrams per square decimeter ofgelatin hardened with 2.96 g. of formaldehyde and 11.25 g. ofdimethylolurea per g. of gelatin. The element was then overcoated withthe nickel (II) hexacyanoferrate (II) sol of example X by skim coatingat 100 F and 9 feet per minute, and hot air dried.

A sample was exposed through a step wedge and line image transparencyfor 10 seconds with a K&M Tri Level Point Source lamp* operated at lever2 at a distance of 50 inches using an ultraviolet filter and a neutraldensity filter of 0.6 optical density. The exposed sample was developedSame as in example XIV, operated at 16 volts. 30 seconds in thedeveloper of example I and activated for 8 seconds in an activatorsolution having the following composition.

3 molar copper (ll) nitrate trihydrate 25 ml. 3 molar potassium bromidel5 ml. 3 molar citric acid 25 ml. 1 molar iron (Ill) nitrate monohydratel0 ml. Water to make L000 ml.

The plate was then rubbed with a 1 percent aqueous dispersion ofcolloidal silica and used on an office duplicator to print offset copiesusing the ink and fountain solution of example I.

EXAMPLE XIX A sample of the coated emulsion of example XV was overcoatedby bathing in a palladium (II) hexacyanoferrate (II) sol prepared asfollows, then drying.

Solution A Water 665 ml. 0.1 molar palladium (ll) chloride (aqueous) 20ml. 0.1 molar potassium citrate (aqueous) 15 ml. Solution B Water 7 2ml. 0.1 molar potassium hexacyanoferrate (ll) 20 ml. Condensationproduct of coconut fatty acid and diethanol amine (l gram per 100 ml.ofalcohol) 8 ml.

Solution A was added rapidly to Solution B at 75 F. with rapid stirring.

The sample was exposed through a step wedge to a 0.0001 sec. flash froman Edgerton, Germeshausen, and Grier Mark Vl exposure unit. The exposedsample was developed for 30 seconds in the developer of example I, waterwashed for 5 seconds, and activated for 15 seconds in an activatorsolution of the following composition.

3 molar copper (ll) nitrate (aqueous) 25 ml. 3 molar potassium bromide(aqueous) l5 ml. 3 molar citric acid (aqueous) 25 ml. Water to make L000ml.

The activated sample was swabbed with the fountain solution of example Iand then with lithographic ink. Good lithographic copies were obtained.

EXAMPLE XX Example XIX was repeated except that rhodium (ll) chloridewas used in place of palladium chloride. Good lithographic copies wereobtained.

EXAMPLE XXI An element prepared as in example X was exposed on aphototypesetting machine having a cathode-ray tube readout operatedunder the condition ordinarily used for exposing phototypesetting film.The exposed sample was developed for 30 seconds in a suitable developingmachine filled with the developer of example I and activated for 8seconds in a suitable processing machine filled with the activator ofexample 1K. The sample was then placed on the office duplicating machineof example I, swabbed with the fountain solution of example I, inkedwith lithographic ink and used to print several thousand offset copiesof good quality on white bond paper.

The embodiments of the invention in which an inclusive property orprivilege is claimed are defined as follows:

1. A photographic element comprising a support bearing a gelatino-silverhalide emulsion layer and in operative association with the surface ofsaid layer a stratum of hexacyanoferrate comprising a heavy metalhexacyanoferrate (ll) or hexacyanoferrate (lIl), said heavy metal beingselected from the group consisting ofcopper (ll), nickel (ll), cobalt(ll), palladium (II), and rhodium (ll).

2. An element according to claim 1, wherein said stratum is in or on thesurface of said emulsion layer.

3. An element according to claim 1, wherein said stratum is on a thinintervening water-permeable protein colloid antiabrasion layercontiguous with the emulsion layer.

4. An element according to claim 1, wherein said hexacyanoferrate is anickel (II), hexacyanoferrate (ll) or (III).

5. An element according to claim 1, wherein said support is ahydrophobic macromolecular organic polymer film.

6. An element according to claim 11, wherein the coating weight of thesilver halide is at least 1 milligram per square decimeter.

7. An element according to claim l, wherein the coating weight of thesilver halide is about 5 to about 50 milligrams per square decimeter.

8. An element according to claim 1, wherein the emulsion is anorthochromatic gelatino-silver halide emulsion.

2. An element according to claim 1, wherein said stratum is in or on thesurface of said emulsion layer.
 3. An element according to claim 1,wherein said stratum is on a thin intervening water-permeable proteincolloid antiabrasion layer contiguous with the emulsion layer.
 4. Anelement according to claim 1, wherein said hexacyanoferrate is a nickel(II), hexacyanoferrate (II) or (III).
 5. An element according to claim1, wherein said support is a hydrophobic macromolecular organic polymerfilm.
 6. An element according to claim 1, wherein the coating weight ofthe silver halide is at least 1 milligram per square decimeter.
 7. Anelement according to claim 1, wherein the coating weight of the silverhalide is about 5 to about 50 milligrams per square decimeter.
 8. Anelement according to claim 1, wherein the emulsion is an orthochromaticgelatino-silver halide emulsion.